1. Field of the Invention
The present invention relates to telecommunications systems, and in particular to a digital telecommunications system having outslot signaling in signal channels in addition to the communication channels and which may possibly include additional inslot signaling within a communication channel, and in which, and more specifically, in connection segments of a connection existing between two telecommunications stations on which no outslot signal channel is available, the outslot signaling is transmitted in an inslot-outband-subchannel of the appertaining communications channel.
2. Description of the Prior Art
Newer developments in telecommunications have led to digital telecommunications systems which provide a conversion of the voice signals into digital signals for the telephone subscribers in the subscriber station and in which a digital telephone connection between the subscriber station and the exchange to which the subscriber station is directly connected can be completed by way of a uniform digital communications channel having a bit rate of, for example, 64 kbit/s (per transmission direction) and, moreover, outslot of the 64 kbit/s communications channel a signaling connection for outslot signaling can constantly exist via an additional signal channel with a bit rate of, for example, 8 kbit/s (per transmission direction), whereby, in addition to outslot signaling, inslot signaling can also be provided within the communications channel (International Switching Symposium, Paris, May 11, 1979, pp. 773-780); in addition to speech, text, data and images can be transmitted via digital subscriber terminals in the 64 kbit/s common channels of such a digital telecommunications system.
In such a digital telecommunications system, there is the possibility that, in terms of exchange orientation, certain subscriber stations do not belong to that exchange to which the appertaining subscriber station is directly connected, but, rather, to a different switching center--via a permenent through-connected connection extending via the switching center; such a network configuration can be given, for example, in a service-integrated digital telecommunications system in that data subscriber stations are only indirectly connected to an appertaining data switching center via permanent through-connected connections extending through telephone switching centers (Telefon Report 11 (1975) 3, pp. 86-90).
Such a connection of a subscriber station to the appertaining switching center, which is only indirect, can lead to the fact that only the common, actual communications channel with the bit rate of, for example, 64 kbit/s is available on a part of the overall connection path, not, however, an additional signal channel as well, so that the same signaling procedures and corresponding interface conditions are not possible for subscriber stations directly connected and for subscriber stations indirectly connected, at least not without further provisions; however, identical signaling procedures and interface requirements can be precisely the things which are required, particularly given subscriber stations which are otherwise identical.